Electrical machines, for example motors and generators, include electrical conductors, a main insulation and a laminated stator core. The main insulation has the purpose of electrically insulating the conductors from one another, from the laminated stator core and from the environment. In the region of the electrical machine, partial electrical discharges can form sparks, which can develop what are called “treeing” channels in the main insulation. As a result of the “treeing” channels, there may be electrical sparkover through the main insulation. A barrier against a partial discharges is achieved by the use of mica in the main insulation, the latter having a high partial discharge resistance. The mica is used in the form of mica particles in platelet form having a conventional particle size of several hundreds of micrometers up to several millimeters, the mica particles being processed to give a mica paper. To increase the strength and to increase the processibility, an electrical insulation tape having a support structure as well as the mica paper is used.
To produce the main insulation, the electrical insulation tape is wound around the conductor and then impregnated with a synthetic resin. The synthetic resin is cured in the presence of a reaction accelerator, conventionally zinc naphthenate, i.e. zinc salts of a mixture of cyclopentanoic acids and cyclohexanoic acids. The mixture is obtained in the distillation of crude oil within a particular temperature range, which may have the effect that, starting from different batches of crude oil, the mixture may also be of different composition from batch to batch. As a result, the curing characteristics of the synthetic resin may likewise vary from batch to batch. It is therefore necessary to prepare each batch of the zinc naphthenate in a complex manner, for example by adjusting its pH, its acid number and its viscosity.
EP 0 198 195 A2 describes zinc octylate as reaction accelerator. U.S. Pat. No. 4,178,274 A describes zinc 2-ethylhexanoate as reaction accelerator. U.S. Pat. No. 3,449,641 A discloses zinc octoate in the presence of an epoxy resin. GB 1 557 641 A describes zinc 2-ethylhexanoate in the presence of an epoxy resin. U.S. Pat. No. 6,190,775 B1 describes a flexible insulation tape. GB 2 019 778 A discloses an impregnated mica film. EP 1 850 460 A2 discloses zinc naphthenate in the presence of an epoxy resin.